The present invention relates to a rotary apparatus which is rotated at high speed, such as a light deflection apparatus using a polygon mirror, or motors.
In the light deflection apparatus rotating at high speed using the polygon mirror as a rotor, or motors rotating at high speed around a rotation axis, a dynamic pressure bearing is provided between a rotational body and an irrotational body, and the high speed rotation is carried out. FIG. 21 is a sectional view showing an example of the rotary apparatus provided with the dynamic pressure bearing. A rotary unit 102 which rotates facing a radial fixed member 111 which is fixed on a support base 103, is radial dynamic pressure rotated in between both members at the radial dynamic pressure bearing portion 112. Further, on both shaft end portions of the radial fixed member 111, a thrust fixed member 113 which forms a perpendicular surface to the shaft of the radial fixed member 111, is provided, and a rotary unit 102 which is rotated being sandwiched between a thrust fixed member 113A and a thrust fixed member 113B, which are positioned at an upper and a lower portions, is thrust dynamic pressure rotated at a thrust dynamic pressure bearing portion 121.
On the radial dynamic pressure bearing portion 112 and/or the thrust dynamic pressure bearing portion 121, a dynamic pressure generating groove formed symmetrically with the bearing surface is provided, and a wind generated by the high speed rotation of the rotary unit 102 is introduced into the dynamic pressure generating groove, and the strong wind pressure is generated from the symmetrically formed dynamic pressure generating groove, and a gap in several .mu.m unit is formed between the radial fixed member 111 and the rotary unit 102, and the resistance between them is decreased, thereby, the high speed rotation is attained at the radial dynamic pressure bearing portion 112. Further, a fine gap is formed also between the thrust fixed members 113A, 113B and the rotary unit 102, and while the rotary unit 102 is floated a very little, the high speed rotation is performed at the thrust dynamic pressure bearing portion 121.
In the conventional rotary apparatus provided with the dynamic pressure generating groove which is symmetrical to the dynamic pressure bearing portion, generally, in order to prevent the contact generated during high speed rotation and to decrease the vibration, the dynamic balance is decreased, however, when the dynamic balance is too small, the unstable phenomenon of the rotation is generated on the contrary. In the conventional rotary apparatus, in the adjustment, the upper limit of the dynamic balance is regulated by the tolerance limit of the vibration, and the lower limit is regulated by the tolerance limit of the stability, and the dynamic balance is corrected so that it is within the range between the regulated upper limit and the lower limit, or the gap between the fixed portion of the radial dynamic pressure bearing portion (radial fixed member) and the rotational body (rotary unit) is appropriately adjusted, thereby, the stability in the high speed rotation is obtained.